Is Time Travel Really Possible?
Before examining the grandfather paradox and parallel universes, a cursory look at time travel is in order. Ever since H. G. Wells wrote The Time Machine in 1895 (and certainly even before that) people have been fascinated by the possibility of time travel. Many yearned to travel back in time to see deceased loved ones or even witness famous world events. Others longed to travel into the future to catch a glimpse of advanced civilizations and technologies. But just ten years after “The Time Machine” was published, a brilliant young scientist showed that the theory of time travel was indeed science and not science fiction.
In 1905, Albert Einstein published the theory of special relativity. This groundbreaking work showed that the faster an object travels, the more that time will slow down. While this idea seemed fantastic at the time, recent experiments with clocks aboard planes have empirically shown those clocks to move slower than timepieces on the ground. In fact, all astronauts have experienced time travel into the future (albeit by a fraction of a second.)
However, the concept of time travel into the past is far more problematic. Although physicists such as Frank Tipler of Tulane University have made great advances with cylinders and time loops, the technology to allow backward time travel may be thousands of years away. In addition to technical difficulties, theoretical physicists and philosophers have noted logical problems that may disallow time travel into the past. The most famous of these is the grandfather paradox.
The Grandfather Paradox
This is a simple summary of the grandfather paradox. Imagine that you travel back in time to visit your grandfather before he met your grandmother. It does not matter which grandfather you visit. Not that anyone would wish to do this, but imagine that you kill your grandfather. Since you did this before he met your grandmother, she never gave birth to one of your parents. And since one of your parents was never born, you were never born. That is the grandfather paradox. (If you choose not to imagine such dastardly deeds, you can go back in time and distract your grandfather at the moment he was to meet your grandmother!)
In any event, one of your parents was never born and neither were you. Yet, here you stand, traveling through time, hanging out with grandpa. This is the essence of the grandfather paradox and people have used this example for years to argue that backward time travel is not logically possible. However, recent theories on parallel universes may give time travel enthusiasts a “time-loophole” to the grandfather paradox.
The concept of parallel universes is highly theoretical with little, if any, empirical proof. In addition, there are a variety of different theories explaining how a multiverse of different parallel universes could exist. For simplicity, assume there are an infinite number of parallel universes. Many people confuse exactly what the word infinity means. Infinity is not a large number. Infinity is not even a number. It is a concept describing an endless quantity. Therefore, if there are an infinite number of parallel universes, then everything that can possibly happen does happen in some universe.
Back to time travel and the grandfather paradox, once again assume you have stopped (in your own way) your grandfather and grandmother from meeting. How is it that you were never born, yet you interact with your grandfather? If there are parallel universes, then each event takes place in a different universe. In universe A, your grandparents met and you were eventually born. In universe B, you stopped your grandparents from meeting and you lived happily ever after in the past. This would enable both events to occur with no contradiction.
Is backward time travel physically possible? Do parallel universes exist? We don’t yet have the answers to these questions. But if parallel universes are out there, then time travel into the past may no longer be inhibited by the grandfather paradox.
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